A
The Cabinet salvaged 2" plywood for the back, top, and sides,
The finished projector is basically a plywood cabinet and some ½" ply for the front panel.
with a lens holder in the face, an internal lighting
system, and an angled front-surface mirror behind
the lens (Figure A).
The mirror serves to flip and invert the image
so that it will appear right-reading on the screen,
and to “fold” the optical path, allowing the cabinet
design to be more compact, and the copy to be
laid flat. The bottom of the box is left open and the
projector simply placed on top of the copy. Focus is
achieved by sliding the lens in and out in its carrier.
The dimensions of your projector cabinet will
depend upon your lens selection, expected copy
size, and desired magnification. A quick way to
come up with a rough layout is to cut out a paper
pattern that represents your “light cone.” The shape
will be an isosceles triangle with the base being the
maximum width of your copy area, and the height
being the effective FL of your lens. Fold the paper
triangle at a 90° angle roughly at the midpoint. The
fold will describe the correct position of the mirror.
Now build your cabinet to dimensions that can
accommodate this pattern. I used scrap and
Assembly
After gluing up the box, I made a lens carrier from
an empty cocktail peanut can with the bottom cut
off. The size and price were about right, and the
metal rim provided a nice finished look when the
can was epoxied into a circular hole cut into the
front panel. To get a nice snug fit in the carrier,
I tightly wrapped the lens barrel in several turns
of black yarn.
For lighting, I installed 2 ceramic lamp bases
high up in the cabinet, 1 on each side of the lens,
and made reflectors out of some mylar insulation
material. I wired them together with a lamp cord,
which exits the back of the cabinet. I’m using a pair
of 23W compact fluorescent bulbs, which give
off the equivalent of 200 W of tungsten light; this
is still pretty dim, but I wanted to avoid the heat
produced by brighter incandescent lamps.
A strategically shaped bank of high-output LEDs
would nicely augment these lights. The entire
inside is painted black to prevent glare from stray
Photography by Steve Lodefink; illustration by Tim Lillis
76 Make: Volume 14
